Stretch wrapping machines are commercially available which automatically wrap a load disposed on a rotatable turntable with a stretchable wrapping material. These machines may be fully automatic, including conveying of the load to and from the turntable by an automated conveyor system or by the use of a lifting device, such as a forklift, which places individual loads on the turntable where fully automated wrapping is performed. Automatic stretch wrapping machines are characterized by a high throughput with an increase in the throughput, lowering of consumption of stretchable wrapping material and a decrease in wrapping time being design goals required for the wrapping of individual loads. Automatic stretch wrapping machines may wrap the load on the turntable with a stretchable wrapping material having a width equal to or greater than the height of the load being wrapped with several turns of the stretchable wrapping material or with a stretchable wrapping material having a width less than the height of the load being wrapped by vertically translating the wrapping material with respect to the height of the load to spirally wrap the load with multiple turns of the stretchable wrapping material.
In an automatic stretch wrapping machine, it is necessary to attach a leading edge of the wrapping material to the load being wrapped during the wrapping cycle and to sever the trailing edge from the supply of stretchable wrapping material and attach the trailing edge of the wrapping material to the load prior to removal from the turntable. The prior art has utilized a number of different techniques for attaching the leading and trailing edges of the wrapping material to the load.
The leading edge of the wrapping material may be gathered into a rope and clamped by a clamp carried by the rotating turntable to retain the wrapping material during initiation of the wrapping cycle. Examples of automatic stretch wrapping machines utilizing this technique are disclosed in U.S. Pat. Nos. 4,271,659, 4,300,326, 4,302,920, 4,432,185, 4,563,863, which is assigned to the Assignee of the present application, and 4,619,102.
U.S. Pat. Nos. 4,077,179, 4,216,640 and 4,235,062 disclose the retaining of the leading edge of the wrapping material during the initiation of the wrapping cycle without roping by clamping ungathered wrapping material. Clamping mechanisms for the wrapping material which do not utilize roping have the disadvantage that the thinness of the wrapping material makes it difficult for the initiation of wrapping to be started under full tension as consequence of the propensity of the thin wrapping material to slip under high applied tension between the jaws of a clamp. Furthermore, the unroped wrapping material is subject to tearing from the grip of the clamp which can cause automatic wrapping of a load to fail requiring reclamping of the wrapping material.
Mechanisms for attaching the trailing edge of the wrapping material to the load at the end of the wrapping cycle include heat sealing of the stretchable wrapping material to the load and the brushing of the full width of the stretchable wrapping material or a gathered width against the load with reliance being placed upon static attraction of the trailing edge to an underlying wrap of the wrapping material. The Assignee's U.S. Pat. No. 4,563,863 discloses the use of a brush for brushing the trailing edge of the wrapping material against the load to secure the gathered trailing edge to an underlying wrap of the material. The assignee's Model 8200AX and 8200CAX automatic stretch wrapping machines include sensors for detecting oversized loads and the height of the load which may be erroneously tripped by a loose trailing edge which can cause a shutdown of wrapping. Shutdowns which require a resetting of the system reduce the efficiency of wrapping and the throughput.
Stretch wrapping machines which rely upon gathering of the full width of the stretchable wrapping material into a rope to clamp the leading edge are limited in the width of the stretchable wrapping material which may be used. As the width of the stretchable wrapping material becomes greater, the diameter of the rope becomes so great that it is not possible to effectively clamp the rope. The center portion of a large diameter rope can pull out from the clamp. In commercially available automatic stretch wrapping machines, it becomes extremely difficult to utilize wrapping material widths greater than a dimension such as 30 inches which rely upon gathering for retention in a clamping mechanism for initiating of wrapping. Furthermore, the Assignee of the present invention has found that its Models 8200CAX and 8200AX, which are in accordance with U.S. Pat. No. 4,563,863, have difficulty gathering wide widths of stretch wrapping material, such as those above 30 inches.
In the Assignee's Models 8200CAX and 8200AX when a wide width of stretchable wrapping material is used, the top edge of the stretch wrapping material is placed under high tension as a consequence of a gathering arm being rotated downward to pull the wrapping material into the clamp carried by the turntable. The loading of high tension on top of the stretchable wrapping material causes the wrapping material at the bottom edge of the width of the wrapping material to be loose or under little tension. The loose stretchable wrapping material may not be completely retained by the clamp when the loose wrapping material is forced into the clamp by the gathering arm. An unclamped loose leading edge of the stretchable wrapping material can interfere with placing full wrapping tension on the load at the beginning of the wrapping cycle. Loose stretchable wrapping material can cause the load size sensors to be tripped erroneously. Additionally, the application of high tension to the top edge of the stretchable wrapping material may cause the stretchable wrapping material feeding mechanism, such as that manufactured in accordance with U.S. Pat. Nos. 4,706,443, 4,590,746 and 4,862,678, which are assigned to the Assignee of the present invention, to be activated to react to the application of high tension to the top edge of the wrapping material to play out additional wrapping material further loosening the bottom edge.
Additionally, cutting of a rope formed by gathering a width of stretchable wrapping material greater than, for example, 30 inches can result in incomplete severing of the full width when the rope is not completely retained within the clamp which results in the stretchable wrapping material being retained by both the clamping mechanism carried by the turntable and to the load which has been wrapped. This condition requires manual intervention for correction which lowers throughput.
Finally, a large diameter rope is subject to being pulled loose from the clamp during initiation of the wrapping cycle especially when an attempt is made to apply full tension to the stretchable wrapping material at the beginning of the stretch wrapping cycle. Pulling loose of a rope from a clamp at the beginning of the stretch wrapping cycle can require manual intervention to attach the loose leading edge which lowers throughput.
It is well known that spiral wrapping of stretchable wrapping material on a load requires an overlap between adjacent turns to be effective which may require three or more inches of wrapping material. As a result of the required overlap, additional stretchable wrapping material is required to wrap a load with a spiral wrap when compared to the stretchable wrapping material required to wrap the load with a wrapping material which is at least as wide as the height of the load. Accordingly, the overall cost of stretch wrapping could be substantially lessened by an automatic stretch wrapping machine having the ability to wrap loads with widths of stretchable wrapping material of wide widths such as greater than 30 inches without spiral wrapping. Stretchable wrapping material is currently available in widths up to 80 inches or more. Prior art automatic stretch wrapping machines which required the use of a spiral wrapping to wrap high profile loads cannot effectively use these greater widths of stretchable wrapping material for performing non-spiral wrapping. This prevents realization of the cost savings: set forth above consequent from non-spiral wrapping. Furthermore, the inability to use wide widths of stretchable wrapping material prevents a higher number of units from being wrapped in a given time period as a consequence of the turntable making a greater number of turns with spiral wrapping to complete the wrapping cycle.